I had the same problem with mine, and I have run into it as well with other "gray faced" Hammarlunds that I have repaired.
Swap out the 6C4 first conversion L.O. tube, It is probably not always oscilating.
Just because it tests good on a tube checker doesnt mean it will work in that circuit. I have had brand new ones that wouldnt oscilate
It seems to also only happen on certain bands. My 170 was dead on 160, go figger.
I have ever bothered to investigate further why this anomoly happens, but it's usually 1 or 2 bands that are affected, all the other ones work OK. You may have to "test / select" the tue that works best (new or used).
The Slab bacon